The present invention generally relates to printed wiring board units, auxiliary substrates for hierarchical mounting, and electronic apparatuses, and more particularly to a printed wiring board unit mounted in a personal digital assistant or a notebook personal computer, an auxiliary substrate for hierarchical mounting used in such a printed wiring board unit, and an electronic apparatus including such a printed wiring board unit.
A miniaturization, multi-functionalization, and advanced features are demanded of the personal digital assistant and notebook personal computer. In order to meet such demands, the printed wiring board unit mounted in the notebook personal computer requires a structure where semiconductor components are mounted with high density in a limited space.
A conventional printed wiring board unit on which semiconductor components are mounted with high density in a limited space has any of the following structures:
{circle around (1)} A structure where the semiconductor components are mounted on both sides of a mother-board printed wiring board.
{circle around (2)} A structure where a multi chip module of the semiconductor components is mounted on a mother-board printed wiring board.
{circle around (3)} A structure where a chip size package of the semiconductor components is mounted on a mother-board printed wiring board.
Further, each of Japanese Lai-Open Patent Application Nos. 6-152096, 3-101188, and 4-278596 discloses a structure where semiconductor components are hierarchically mounted on a printed wiring board for high-density mounting.
The structure where the semiconductor components are mounted on both sides of a mother-board printed wiring board requires the mother-board printed wiring board to have parts for mounting the semiconductor components on both upper and lower surfaces of the mother-board printed wiring board. Further, this structure requires the mother-board printed wiring board to increase in size if the number of components increases.
The structure where a multi-chip-module printed wiring board is mounted requires advanced technology to produce the multi-chip-module printed wiring board, thus increasing the production costs of the printed wiring board unit.
In the case of employing the chip size package, wiring on the mother-board printed wiring board becomes too dense so that the production costs of the printed wiring board are raised.
In the case of the structure where the semiconductor components are hierarchically mounted on a printed wiring board, a group of lower semiconductor component pads to be connected to the terminals of a lower semiconductor component are arranged inside a group of upper semiconductor component pads to be connected to the terminals of an upper semiconductor component on the printed wiring board so that the groups of the lower and upper semiconductor component pads are substantially concentric with each other, and wiring patterns extending from the lower semiconductor component pads extend outward through spaces each formed between each adjacent ones of the upper semiconductor component pads.
The number of the terminals of semiconductor components is increasing with advanced features of a notebook personal computer. Therefore, a pitch between each adjacent ones of the upper semiconductor component pads becomes shorter so as to produce a narrower space therebetween. This makes it difficult to pass the wiring patterns extending from the lower semiconductor component pads through the spaces between the upper semiconductor component pads. None of the above-described Japanese Laid-Open Patent Application Nos. 6-152096, 3-101188, and 4-278596 discloses any device for passing wiring patterns through spaces between adjacent pads. Therefore, it is difficult to apply any of structures disclosed in the above-described Japanese Laid-Open Patent Application Nos. 6-152096, 3-101188, and 4-278596 to semiconductor components with a large number of terminals.
It is a general object of the present invention to provide a printed wiring board unit, an auxiliary substrate for hierarchical mounting, and an electronic apparatus in which the above-described prior-art disadvantages are eliminated.
A more specific object of the present invention is to provide a printed wiring board that realizes hierarchical mounting of components on a printed wiring board without wiring patterns being formed too densely on the printed wiring board.
This object of the present invention is achieved by a printed wiring board unit, wherein a first component is mounted on a printed wiring board, an auxiliary substrate for hierarchical mounting is mounted next to the mounted first component on the printed wiring board, a second component larger in size than the first component is mounted above the first component, the second component being supported on the auxiliary substrate for hierarchical mounting with terminals of the second component being connected thereto, and the auxiliary substrate for hierarchical mounting has component pads on an upper surface thereof, the pads being connected to the terminals of the second component, printed wiring board pads on a lower surface thereof, the printed wiring board pads being connected to pads on the printed wiring board, and includes ground and power supply layers inside thereof, wherein the component pads and the printed wiring board pads are electrically connected, the printed wiring board pads are decreased in number with component ground terminals included in the component pads and connected to a plurality of ground terminals of the second component being gathered by being connected to the ground layer and component power supply terminals included in the component pads and connected to a plurality of power supply terminals of equal potentials of the second component being gathered by being connected to the power supply layer, and the printed wiring board pads are more dispersed than the component pads.
According to the above-described printed wiring board unit, a gap space between adjacent pads on the printed wiring board which gap space corresponds to the second component is widened so that a wiring pattern extending outward on the printed wiring board from a pad connected to the first component passes through the gap space without difficulty.
Another more specific object of the present invention is to provide an auxiliary substrate for hierarchical mounting used for hierarchical mounting of components on a printed wiring board without wiring patterns being formed too densely on the printed wiring board.
This object of the present invention is achieved by an auxiliary substrate for hierarchical mounting having component pads on an upper surface thereof, the component pads being connected to terminals of a second component larger in size than a first component mounted on a printed board, and printed wiring board pads on a lower surface thereof, the printed wiring board pads being connected to pads on the printed wiring board, and including ground and power supply layers inside thereof, wherein the component pads and the printed wiring board pads are electrically connected, the printed wiring board pads are decreased in number with component ground terminals included in the component pads and connected to a plurality of ground terminals of the second component being gathered by being connected to the ground layer and component power supply terminals included in the component pads and connected to a plurality of power supply terminals of equal potentials of the second component being gathered by being connected to the power supply layer, and the printed wiring board pads are more dispersed than the component pads.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.